Background
The authors write that "Ocean-Atmosphere Global Climate Models (OAGCMs) have become indispensable tools for the climate sciences" and that "many efforts have been made to improve [them] in recent years," noting that" the Climate Forecast System version 2 (CFSv2) model is one example of such progress," which they then go on to describe in considerable detail.

What was done
In the words of Silva et al., "the present study examined the area-average skill over the continents, the interannual variability, the global-mean state, and the main patterns of variability over the Equatorial Pacific and extratropics in both hemispheres produced by the CFSv2 model," which was done by comparing the model's hindcasts for Dec-Jan-Feb (DJF) and Jun-Jul-Aug (JJA) seasons of the 1983-2010 period with both "observations and reanalyses."

What was learned
The five Brazilian scientists report that (1) "at the 0-month lead time ... large biases occur over the oceans," that (2) "improvements in CFSv2 were not enough to eliminate the double-ITCZ [Intertropical Convergence Zone] bias during DJF," that (3) there is a "warm SST [sea surface temperature] bias over eastern oceans during DJF and JJA," that (4) for JJA there is an "SST cold bias over the central-equatorial Pacific," that (5) "during DJF CFSv2 presents a cold bias in the troposphere, mainly over the central-eastern North Pacific," that (6) there is a "strengthening of the subtropical jet that leads to precipitation overestimations by the persistence of low pressures over subtropical and mid-latitude regions," that (7) "CFSv2 shows large precipitation biases over the eastern South Africa and Oceania," that (8) there is a "wind-stress bias in the tropics," that (9) "errors in the simulated Aleutian low seem to degrade the simulated NAM [Northern Annular Mode]," that (10) "the wave pattern associated with the SAM [Southern Annular Mode] is not well reproduced by CFSv2," that (11) there are "biases in the upper-level zonal wind over the tropics and mid-latitudes of the Southern Hemisphere," and that (12) "the major spatial features related to the shape and orientation of SAM are not properly captured by CFSv2."

What it means
Silva et al.'s "overall evaluations" thus lead them to conclude that "further investigations are still needed," and they say that these projected studies "should be carried out to help in understanding in further details the reasons for the CFSv2 deficiencies." We couldn't agree more. But will the conducting of such studies ever end???